One of the interesting things about the Android operating system is the interconnection it has with several other online services. People using the same Gmail email address, the one used to set up their android device, on such online services often find their data synced with their device.
The above lines seem confusing but the following example will help you understand the point being made, better. I have been with my Galaxy Nexus for almost a year and initially when I started using it, I found my pictures from DropBox, and Picasa Web Albums in the Gallery app. Strange it was, but actually this is how the these services find a connection between them and the android OS.
Now this turned out to be very helpful for me as my data from Dropbox and Picasa was present right there in the Gallery app, and I was able to access them anywhere and anytime. But the catch here is that they were only available when my device was connected to the internet. So what if I need these pictures to be available in offline mode?
Follow the guide given below:
Step 1: Launch the gallery app.
Step 2: Tap on the settings button present on the top right section of the screen. On the drop down menu, select Make Available Offline.
Step 3: On the next screen, you will be presented with all the available albums. All you have to do is select the online albums and press the Done button. All the selected albums will be downloaded to your device shortly thereafter and then you will have access to them locally.
The best piece of advice here is that do not use this feature unless you are on a Wi-Fi network. Downloading online albums on mobile data could incur some hefty costs. So it is recommended that you download them only when a wi-fi network is available as the pictures will weigh enough.